The present invention relates to the field of measurement systems, and, more particularly, to optical position determining systems and related methods.
There are many applications in which it is important to know the relative position of one object with respect to another. For example, in automated manufacturing processes using robots, the position of the robot must be accurately controlled to ensure that the position on a work piece at which a fastener is being placed, a weld is being made, etc., is correct.
To obtain precise accuracy in applications where most, if not all, six degrees of freedom (i.e., elevation (or vertical position), azimuth (or lateral position), range (or distance), pitch, yaw, and roll) must be accounted for, computer numerical control (CNC) systems may be used with machine vision and/or optical devices. While such systems may be capable of providing very accurate positional measurements, they are generally relatively large, complex, and costly to implement. As such, these systems may not be practical in some applications where space or cost constraints are tight.
Other less complicated sensors may be used in some applications to measure multiple degrees of positional freedom between objects. For example, inductive or capacitive sensors may be used to determine whether two objects are displaced from one another laterally, vertically, and/or in distance (i.e., range). Yet, these sensors typically require a very close proximity between the two objects. Moreover, they do not provide other positional degree of freedom information such as pitch, yaw, and roll.
Another example of a position determining system may be found in U.S. Pat. No. 5,974,365 to Mitchell. This patent discloses a system for position measurement and alignment of one object relative to another, particularly the alignment of two spacecraft for docking. To this end, the system includes a linear optical detector array sensor on the first object and a predetermined target pattern (i.e., a series of right-side up and upside down xe2x80x9cVxe2x80x9ds) on the second object. Based upon the image formed by the target pattern on the detector, the six degrees of freedom of the second object are calculated by a microprocessor using certain algorithms. Another somewhat related system for use in docking spacecrafts is disclosed in U.S. Pat. No. 3,491,969 to Muldoon.
Other position measuring systems may be appropriate where not all six degrees of freedom of an object need be measured. For example, U.S. Pat. No. 5,984,370 to Okuda et al. is directed to an inclination monitoring system for adjusting the inclination of an objective lens during the manufacture of an optical disk drive. To monitor the inclination the objective lens, the system includes a light emitting unit, a beam splitter, a converging lens, a charge-coupled device (CCD), and a data processing device and display therefor. The light emitting device is driven to emit a light beam which has a slightly larger diameter in cross section than a diameter of the objective lens. The light beam reflects off the beam splitter toward the objective lens. A flat portion of the objective lens reflects a part of the beam which passes through the beam splitter and is focused by the converging lens on the CCD. The CCD outputs an image signal to the data processing device, which causes an image of the reflected beam focused on the CCD to be displayed on the display. An operator may thus adjust the angle of inclination (i.e., pitch and yaw) of the objective lens until the image is centered at the correct location on the display.
Unfortunately, there are other positioning or alignment applications which would benefit from greater accuracy, and while being relatively straightforward to implement.
In view of the foregoing background, it is therefore an object of the present invention to provide an apparatus and related methods for determining relative positioning of objects in multiple degrees of freedom which are relatively cost effective and may be implemented in applications where space is limited.
These and other objects, features, and advantages in accordance with the present invention are provided by an apparatus for determining relative positioning of first and second objects being relatively movable using a laser source and a target optical element. The apparatus may include the laser source carried by the first object for generating a source laser beam toward the second object, and the target optical element may be carried by the second object for generating a first reflected beam and a second diverging reflected beam from the source laser beam. Furthermore, a detector may be carried by the first object for detecting the first reflected beam and the second diverging reflected beam. A controller may also be connected to the detector for determining a range between the detector and target optical element based upon a size of the second diverging reflected beam. In some embodiments, the controller may also determine at least one other positional degree of freedom quantity based upon the first reflected beam and the second diverging reflected beam.
Accordingly, the controller may determine at least one of alignment error data and second object position data based upon the determined range and/or the determined at least one other positional degree of freedom quantity. Such data may then advantageously be used for correcting the relative positioning between the first and second objects, if necessary, or for updating motor drive position encoding tables, for example.
In particular, the controller may determine the at least one other positional degree of freedom quantity by calculating a first centroid for the first reflected beam and a second centroid for the second diverging reflected beam, and determining positions of the first and second centroids. Additionally, the controller may define vertical and lateral reference coordinates, and the at least one other positional degree of freedom quantity may be at least one of vertical displacement, lateral displacement, pitch angle, and yaw angle.
The controller may further define a first roll angle reference pattern, and the target optical element may have a pattern generator associated therewith for imparting a second roll angle reference pattern to one of the first reflected beam and second diverging reflected beam. As such, the at least one other positional degree of freedom quantity may be a roll angle determined based upon the first and second roll angle reference patterns. Particularly, in some advantageous embodiments the pattern generator may be a diffractive optical element (DOE) associated with a front or rear surface of the target optical element. Similarly, the second diverging beam may include a plurality of diffracted rays.
By way of example, the target optical element may include a lens having a flat rear surface and a convex front surface. Moreover, a partially reflective coating may be on the front surface of the lens and a more reflective coating may be on the rear surface. The target optical element may also include a corner cube.
In addition, the laser source may include a laser emitter and a beam splitter downstream therefrom, and the detector may include an array of pixel elements. A reference indicator may also be carried by the first object for aligning the laser source, and the controller may control the laser source to provide a desired signal level at the detector. Further, an optical filter may also be associated with the detector.
A method aspect of the invention is for determining relative positioning of relatively movable first and second objects. The method may include generating a source laser beam toward the second object, and generating a first reflected beam and a second diverging reflected beam from the source laser beam using a target optical element carried by the second object. The method may further include detecting the first reflected beam and the second diverging reflected beam using a detector carried by the first object. Accordingly, a range between the detector and target optical element may be determined based upon a size of the second diverging reflected beam. Furthermore, at least one other positional degree of freedom quantity may also be determined based upon the first reflected beam and the second diverging reflected beam.